Contiguity and conditioned reinforcement in probabilistic choice.
A five-second pause before a reinforcer cue cuts its strength, so deliver conditioned reinforcers without gaps.
01Research in Context
What this study did
Martin et al. (1997) worked with pigeons in a two-key choice setup. One key gave food half the time. The other key gave food every time.
The catch: before each food delivery, a brief light came on. The team added a five-second gap between the light and the food. They wanted to see if the gap made the light less powerful as a reinforcer.
What they found
Without the gap, birds pecked the 50% key too much. After the gap was added, most birds switched to the sure-thing key.
The short delay weakened the light’s pull, showing the light worked as a conditioned reinforcer.
How this fits with other research
Anonymous (1995) ran the same birds-and-gap test two years earlier and saw the same drop in risky choice. The result is solid across labs.
Mazur et al. (1992) also used lights with probabilistic food, but they varied the number of links instead of adding a gap. Preference still shifted when the conditioned stimulus lost value, backing the same idea with a different twist.
Kirkpatrick-Steger et al. (1996) swapped food lights for token lights and found the same rule: delay the token exchange, not the token delivery, and choice moves away. The gap trick works for tokens too.
Why it matters
You now have lab proof that a tiny delay before a reinforcer cue can slash its power. In practice, deliver praise, tokens, or edible stamps right away. If you must wait, keep the gap under one second. Longer pauses let the value leak out, just like the five-second gap did for the pigeons.
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02At a glance
03Original abstract
In a baseline condition, pigeons chose between an alternative that always provided food following a 30‐s delay (100% reinforcement) and an alternative that provided food half of the time and blackout half of the time following 30‐s delays (50% reinforcement). The different outcomes were signaled by different‐colored keylights. On average, each alternative was chosen approximately equally often, replicating the finding of suboptimal choice in probabilistic reinforcement procedures. The efficacy of the delay stimuli (keylights) as conditioned reinforcers was assessed in other conditions by interposing a 5‐s gap (keylights darkened) between the choice response and one or more of the delay stimuli. The strength of conditioned reinforcement was measured by the decrease in choice of an alternative when the alternative contained a gap. Preference for the 50% alternative decreased in conditions in which the gap preceded either all delay stimuli, both delay stimuli for the 50% alternative, or the food stimulus for the 50% alternative, but preference was not consistently affected in conditions in which the gap preceded only the 100% delay stimulus or the blackout stimulus for the 50% alternative. These results support the notion that conditioned reinforcement underlies the finding of suboptimal preference in probabilistic reinforcement procedures, and that the signal for food on the 50% reinforcement alternative functions as a stronger conditioned reinforcer than the signal for food on the 100% reinforcement alternative. In addition, the results fail to provide evidence that the signal for blackout functions as a conditioned punisher.
Journal of the experimental analysis of behavior, 1997 · doi:10.1901/jeab.1997.68-317